The present invention relates to a molding machine having a plurality of drive mechanisms driven by servo motors and a control method of the molding machine. The present invention is suitable for an injection molding machine and a molding machine, for example, a two-material or two-color molding machine including a plurality of drive-mechanisms of the same type.
A motor-driven injection molding machine will be explained with reference to FIG. 1. The motor-driven injection molding machine includes a motor-driven injection device driven by servo motors. In the motor-driven injection device, a screw is moved forward and rearward by converting the rotational motion of the servo motor into a linear motion by for example, a ball screw and a nut.
In FIG. 1, the rotation of an injection servo motor 51 is transmitted to a ball screw 52. A nut 53 is fixed to a pressure plate 54 and moved forward and rearward by the rotation of the ball screw 52. The pressure plate 54 can move along a guide bar 56 fixed to a base frame 55. Although a plurality of guide bars are ordinarily provided, only one guide bar is shown here. The forward and rearward movement of the pressure plate 54 is transmitted to a screw 60 through a bearing, a load cell (any of them is omitted), and an injection shaft 57. The screw 60 is disposed so that it can rotate in a heating cylinder 61 and moves in an axial direction. A resin supply hopper 62 is disposed to the heating cylinder 61 corresponding to the rear portion of the screw 60. The rotational motion of a metering servo motor 63 is transmitted to the injection shaft 57 through a coupling member such as a belt, a pulley, and the like to rotate the screw 60. That is, the screw 60 is rotated by driving the injection shaft 57 in rotation by the rotation servo motor 63.
The heating cylinder 61 having the screw 60 disposed therein and the hopper 62 are called a plasticizing device. Although the plasticizing device is ordinarily locked to the base frame 55, when the device is unlocked, it can be moved forward and rearward in the axial direction of the screw 60 by a motor 58.
Next, a motor-driven mold clamping device driven by servo motors will be explained. The motor-driven mold clamping device has a fixed platen 72 having a fixed mold 71 attached thereto, a plurality of tie-bars 73, and a movable platen 75 having a movable mold 74 attached thereto. The motor-driven mold clamping device further has two arms 76 whose one ends are coupled with the movable platen 75, a toggle support 77, a mold clamping servo motor 78, a ball screw 79, a cross head 80 having a ball nut threaded with the ball screw 79, and the like.
The rotational motion of the servo motor 78 is converted into the linear motion of the cross head 80 through the ball screw 79. The linear motion of the cross head 80 is converted into the forward and rearward motion of the movable platen 75 through a toggle mechanism composed of the cross head 80, toggle levers 81a and 81b, and the arms 76. When the movable platen 75 travels forward, causes the movable mold 74 to come into contact with the fixed mold 71 and further travels forward, the tie-bars 73 are extended and generate mold clamping force. Reference numeral 82 denotes a molded product eject motor.
The toggle support 77 is ordinarily locked to the fixed platen 72 through the tie-bars 73 also in the mold clamping device. However, when the toggle support 77 is unlocked, an element including a toggle mechanism, and the movable platen 75 can be moved in a mold open/close direction by a mold thickness adjust motor 83.
As can be understood from the above description, in the motor-driven injection molding machine, a servo-controlled drive mechanism includes four drive mechanisms, that is, an injection drive mechanism 91, a metering rotation drive mechanism 92, an ejector drive mechanism 93, and a mold opening/closing drive mechanism 94 as shown in FIG. 2. Note that these drive mechanisms may be called drive shafts. In any case, each of the drive mechanisms is composed of a servo motor as a drive unit and a servo controller as a drive controller, for example, DSP (digital signal processor) for controlling the servo motor.
In general, an injection molding machine makes a molded product through a plurality of processes of metering process—mold closing process—injection process—mold clamping process—dwelling process—mold opening process—eject process.
Heretofore, the data such as the drive command values, the detected values, and the like of the injection drive mechanism 91, the metering rotation drive mechanism 92, the ejector drive mechanism 93, and the mold opening/closing drive mechanism 94 are transmitted from the respective servo controllers thereof to the servo controllers of all the other drive mechanisms through a main controller 90 as an overall controller. The detected values detected by the detectors, which are attached to the drive units constituting the drive mechanisms or attached to driven units driven by the drive units, are input to the servo controllers as drive controllers. The servo controllers calculate the differences between the command values from the main controller 90 and the detected values input thereto and control the drive units based on the differences. The main controller 90 is realized by, for example, CPU (central processing unit). Heretofore, the main controller 90 controls the four drive shafts to establish synchronization among them at a four axis control processing speed.
For example, the data are transmitted from the metering rotation drive mechanism 92, the ejector drive mechanism 93, and the mold opening/closing drive mechanism 94 to the injection drive mechanism 91 through the main controller 90 at all times according to the processing speed of the main controller 90 to establish synchronization. In contrast, the data is transmitted from the injection drive mechanism 91 to the main controller 90. That is, the detected value of the injection drive mechanism is transmitted to the other three drive mechanisms through the main controller 90 at all times, thereby a synchronous control is executed such that drive timings are correctly in coincidence with each other among the four drive mechanisms. This is also the same as to the other three drive mechanisms.
Next, a two-material molding machine will be explained with reference to FIGS. 3 to 6. Note that it can be assumed that a two-color molding machine has the same arrangement as that of the two-material molding machine. Ordinarily, the two-material molding machine has two injection devices mounted on a frame with respect to one mold clamping device shown in FIG. 1 and molds a plurality of molded products by respective cavities of front and rear sides. FIGS. 3-6 show only the arrangement of the two-material molding machine in the vicinity of a mold thereof.
In FIG. 3, reference numeral 121 denotes a fixed platen, 122 denotes a movable platen moved forward and rearward by a mold opening/closing drive mechanism (not shown). The fixed platen 121 has a fixed mold 123 attached thereto, and the movable platen 122 has a movable mold 124 attached thereto through a reversing device 125. Reference numeral 128 denotes a first heating cylinder for melting a resin as a first material, and reference numeral 129 denotes a second heating cylinder for melting a resin as a second material. Ordinarily, the first heating cylinder 128 is called a front side, and the second heating cylinder 129 is called a rear side. It is needless to say that the type of the first material resin is different from that of the second material resin. The first molten resin material and the second molten resin material are injected from a first injection nozzle 130 and a second injection nozzle 131, respectively and fill the cavities formed between the fixed mold 123 and the movable mold 124.
A molding operation will be executed as described below. On the first heating cylinder 128 side, the first molten resin material injected from the first injection nozzle 130 fills the cavity and molds a first molded product portion 135. On the second heating cylinder 129 side, the second molten resin material injected from the second injection nozzle 131 fills the cavity and molds a second molded product portion 136 on the surface of the first molded product portion 135 molded by the previous shot.
Subsequently, as shown in FIG. 4, the mold opening is executed, and a sprue runner 138 is removed from the first molded product portion 135 on the first heating cylinder 128 side. In contrast, on the second heating cylinder 129 side, a molded product 137 composed of the first molded product portion 135 and the second molded product portion 136 is ejected from the mold.
Next, as shown in FIG. 5, the movable mold 124 is reversed by the reversing device 125, thereby the first molded product portion 135 is moved from the first heating cylinder 128 side to the second heating cylinder 128.
Subsequently, as shown in FIG. 6, the mold closing and the mold clamping are executed, and, on the first heating cylinder 128 side, the first molten resin material injected from the first injection nozzle 130 fills the cavity and a first molded product portion 135 is molded. In contrast, on the second heating cylinder 129 side, the second molten resin material injected from the second injection nozzle 131 fills the cavity, and a second molded product portion 136 is molded on the surface of the first molded product portion 135 molded by the previous shot.
As apparent from the above description, a multi-material or multi-color molding machine includes the same type of a plurality of drive mechanisms. The two-material or two-color molding machine has injection drive mechanisms, metering rotation drive mechanisms, and ejector drive mechanisms provided on front and rear sides, respectively. A mold opening/closing drive mechanism and a reversing drive mechanism are used commonly on the front and rear sides. Accordingly, the two-material or two-color molding machine includes the eight drive mechanisms.
When it is intended to realize the synchronous control of the eight drive mechanisms by a single main controller, a highly performance main controller having a high processing speed is required to establish synchronization among the eight drive mechanisms at a processing speed satisfying the performance of the two-material or two-color molding machine, which increases a cost. That is, when eight axes are synchronized with each other simultaneously by the single main controller, a highly performance main controller having a high processing speed is required.
In contract, a multi-material or multi-color molding machine using two main controllers is proposed to control front and rear sides, respectively. In this case, a third main controller is further required to synchronize front and rear side drive mechanisms with each other, thereby a cost is increased.